1. Field Of The Invention
The present invention relates generally to apparatus for collecting well fluid samples, and more particularly, but not by way of limitation, to apparatus for simultaneously collecting multiple pressurized well fluid samples suitable for laboratory PVT analysis.
2. Description of The Prior Art
Often during the testing of an oil or gas well it is desirable to trap a sample of the well fluid downhole. The prior art includes many devices which are useful to take such samples. The sampling devices may either be tubing conveyed or wireline conveyed and can be actuated in any number of ways.
One often preferred sampling procedure utilizes a tubing conveyed sampling device which is actuated in response to changes in well annulus pressure. Typical examples of such annulus pressure responsive sampling devices are described in U. S. Patent Nos. Re. 29,562; Re. 29,638; 3,858,649; 4,047,564; 4,063,593; 4,064,937; 4,270,610; 4,311,197; 4,502,537; 4,553,598; and in United Kingdom Patent Application GB No. 2132250A.
For the most part, these prior devices have been unsuitable for laboratory PVT analysis for two reasons. First, they are large and heavy and difficult to transport to and handle in the laboratory. Second, they often will leak off gas pressure so that true downhole conditions cannot be recreated in the laboratory.
One example of a sampling apparatus capable of obtaining a pressurized sample suitable for laboratory PVT analysis is shown in U. S. Pat. No. 4,665,983 to Ringgenberg, and assigned to the assignee of the present invention. The Ringgenberg device traps a sample in an annular space 400 as depicted in FIG. 2A thereof.
Another device recently introduced for obtaining pressurized samples suitable for PVT laboratory analysis is that marketed by the Schlumberger Company as its FLO-STAR brand sample chamber as illustrated in Schlumberger brochure SMP-4610 (4 87). The Schlumberger device also utilizes an annular sample chamber defined within the tool housing.
Another feature which is desirable in a sampling device, and which is found in both the Ringgenberg and Schlumberger devices, is that the sample chamber have a full opening bore that remains open even after the sample chamber has been closed to trap a sample. This permits standard perforating guns, actuating devices and the like to be passed through the sample chamber after the sample has been taken, or in the event that the sample chamber is prematurely actuated and closed.
Another desirable feature which is found in the Ringgenberg device is the incorporation of a time delay means which provides a time delay between the actuation of the device and the final closure of the sampler. This permits the sampling device to be placed in a well test string below a tester valve which controls flow of well fluid through the test string. The taking of a shut-in fluid sample is accomplished by first increasing annulus pressure to open both the tester valve and to actuate the sampler, and then releasing a portion of the annulus pressure to close the tester valve before the sample chamber has itself closed. When this occurs, the sample obtained by the sampling chamber will be a shut-in sample as opposed to a flowing sample.
Although both the Ringgenberg and Schlumberger devices are capable of obtaining pressurized well fluid samples suitable for laboratory PVT analysis, they both have the significant disadvantage that the sample is trapped in an annular chamber defined within the tool housing, and the entire tool housing must be transported to the laboratory. Typically, the tool housing will have an outside diameter on the order of five to five and one-half inches, and the tool will have a length on the order of six to seven feet. The weight of the tool and the contained sample will typically be on the order of eighty pounds, thus providing a very large and heavy apparatus which must be transported to the laboratory. Furthermore, laboratory procedures may require the heating of the entire mass of the tool to bottom hole temperatures for analysis purposes.
The prior art does include smaller sampling devices, but these have been wireline conveyed samplers rather than tubing conveyed samplers. One example of such a wireline conveyed sampler is the Ruska subsurface sampler model 1200 which is designed to trap pressurized samples for laboratory PVT analysis. The use of wireline devices is often undesirable, however. It is difficult to seal around a wireline and thus there is a safety problem when taking wireline samples on a flowing well. Also, a significant expense is incurred in bringing wireline equipment and operators to the well site.